Internal use part

The first part consists of fields that the resource manager library uses to:

determine the type of message sent from the client

validate (ensure that the message is not spoofed)

track access mode (used by helper functions)

To keep things simple, I recommend that you always use the
helper functions (the iofunc_*_default() ones) in all connect
functions.
These will return a pass/fail indication, and after that point, you
can then use the "End-user parameters" members within the connect function.